The present invention relates to an ultrasonic blood flow sensing apparatus incorporating an ultrasonic diagnosis device using ultrasonic tomography and a Doppler blood flow meter using an ultrasonic Doppler method.
The Doppler flow meter has not been used frequently in diagnosis because it cannot accurately isolate on a specific part of a living body at which a blood flow measurement is desired. Recently, a proposal to overcome this problem, as described in papers at the 34th Japan Ultrasonic Medical Society page 7, published 1978, combines a blood flow meter and an ultrasonic diagnostic apparatus using ultrasonic tomography, enabling an operator to accurately specify a location of an affected part of a living body for blood flow measurement. The approach will be described briefly. In this blood flow sensing apparatus, an ultrasonic wave is transmitted, by a transducer probe, into a subject under blood flow measurement. Echoes returned from the inside of the subject are received by the probe. Of the echoes received, only the echoes reflected from a specific or affected part of the subject, in which the blood flow is to be measured, are sampled, and the sampled echoes are passed through a band pass filter where the Doppler frequency shift of the echoes is obtained. The Doppler frequency shift thus obtained is treated as blood flow data because it has a proportional relationship to a velocity of the blood flow. A signal representing the Doppler frequency shift is subjected to frequency analysis by a frequency analyzer. The analyzed signal is displayed on a screen of a display unit in which the abscissa coordinate represents time and the ordinate represents a velocity of blood flow proportional to the Doppler frequency shift. Incidentally, the frequency analyzer used is, for example, a fast Fourier transformer (FFT) frequency analyzer capable of processing 128 data items within 2 msec., as described in bulletin in Television Society Vol. 35, No. 1, page 2, 1981.
The prior blood flow sensing apparatus measures and displays an average velocity of blood flow (referred to as an instantaneous average blood flow) averaged in a time range from the start of the blood flow measurement to a proper time point. For securing an accurate diagnosis, however, an average blood flow for one minute, or for one to several cardiac cycles prior to the present time point is required. The former and latter blood flows will be referred to as an average per-minute blood flow and an average per-cardiac cycle blood flow, respectively.